Rotation stages are opto-mechanical devices which hold optical components, such as, for example, polarizers, waveplates, filters, retarders, prisms, optical elements, and optical fibers, and rotate them to specific angular orientations. The rotation stage must perform the precise rotation, and must allow the user to determine the exact angle of rotation. Rotation stages allow for continuous rotation through 360.degree., and the angular position is indicated generally by a vernier scale.
Even though a continuum of angular orientations are available with conventional rotation stages, in many applications, the only angles which are of interest are 0.degree., 45.degree., and 90.degree., and no other angles. Thus, in many applications, a continuum of angles is unnecessary.
Drawbacks exist with respect to conventional rotation stages. It is difficult, especially when small rotation stages are employed, to measure the rotation angle accurately. For example, it is possible to resolve about 0.5.degree. of angle on a stage having a diameter of 1 inch. For 0.1.degree. accuracy, it is necessary to use larger and more expensive stages. Also, measurements made with conventional rotation stages not always are repeatable. Conventional rotation stages also are subject to human error in that reading a small vernier scale can be confusing, and may be very difficult in low-light conditions. In addition, all conventional rotation stages suffer from backlash and other effects which can compromise the accuracy of the measurement.